Gene detection involves detecting various signals upon the hybridization of target genes to probes. Hybridization is a method for detecting a target gene sequence by exploiting the specific binding that occurs between genes with complementary base sequences (hybridization), which is a technique that has been applied in Southern hybridization, DNA microarray, and the like.
The double-stranded configuration that is produced by such hybridization depends on the environmental temperature. Given that the binding force varies according to temperature, double-stranded DNA can dissociate into single-stranded form at temperatures beyond a certain temperature (Tx). This specific temperature is unique for each probe because it is determined by probe conditions, such as the content ratio of the four types of bases as well as the number of bases forming the probe, and environmental conditions, such as the salt concentration of the solution. Only genes having a sequence that is entirely complementary to the probe will form double strands with the probe at the temperature Tx.
The greater the number of non-probe complementary bases in the sequence of the target gene, the lower the temperature Tx. The temperature must therefore be controlled during measurement in order to detect subtle variations in base sequence in the hybridization method.
In conventional gene detection systems, a solution in which the target gene has been dissolved is injected into a container covered on the outside with a heat insulating member, hybridization is then brought about as the solution is maintained at a specific temperature below Tx, and double strands are subsequently detected as a Peltier element or the like is used to heat the solution and keep the temperature at Tx, or double strands are detected after being washed with a washing solution which is at the temperature Tx.
However, because the entire solution injected into the container must be heated or cooled in conventional detection devices, the problem arises that the large amount of solution that is heated or cooled takes a longer time to reach the target temperature, resulting in a more time-consuming detection process.
Furthermore, because only the solution injected into the container is heated or cooled in conventional gene detection devices, another resulting problem is that heat is released or absorbed at the surface of portions of the probe-immobilizing support that are not in contact with the solution, making it impossible to properly control the temperature at the surface of the portions of the probe-immobilizing support that are in contact with the solution. The temperature can be particularly difficult to control when the probe-immobilizing support is made of a material with high thermal conductivity.
Although the optimal temperature Tx for the double strand configuration must be properly established for the detection of SNP (single nucleotide polymorphisms) and the like, the problem arises that it is difficult to make subtle adjustments in temperature with the kind of conventional gene detection device in which the entire solution is heated or cooled.
Furthermore, because the temperature of the solution is controlled in conventional gene detection devices, only one temperature can be set per detection cycle. When a plurality of probes having different gene sequences are immobilized on the probe-immobilizing support side, each probe will have a different Tx, but it is not possible to set a plurality of temperatures per detection cycle. Yet another resulting problem, therefore, is that the detection process takes an even longer time when a plurality of probes are immobilized because the detection process must be carried out each time at a different temperature Tx.